Previously in hopper car construction a void space has been located in the lower portion of the car between each of the adjacent hoppers. This void space represents a loss of potential volumetric carrying capacity of the car.
However, one of the reasons for this void area is the need for hopper slope sheets to extend downwardly to provide easy flow into outlet for discharge of lading from the hopper.
These void areas have not been disadvantageous for the transport of many ladings because the density of most ladings is such that even with the void area, when the car is loaded, the loaded weight is equal to or close to the maximum allowable car weight of 263,000 pounds.
However, with the advent of new, low density ladings, particularly low density plastic pellets, the car can be fully loaded with a low density lading and the car weight is still considerably below the maximum allowable weight.